The inventin relates to a process for stitching a buttonhole, and more particularly to a process for stitching, by means of a zigzag sewing machine, a buttonhole of pigeon-eye type comprising a pattern A of first bar-tack stitches, a pattern B of first line-tack stitches, a pattern C of stitches surrounding the pigeon-eye buttonhole, a pattern Ba of second line-tack stitches and a pattern Aa of second bar-tack stitches as shown in FIG. 1, produced in the order named.
FIGS. 2A through 2C show the order in which this type of buttonhole stitches is produced with the zigzag sewing machine. If the sewing machine operator operates a pattern selecting switch designating the combination of patterns A and B and then drive the sewing machine, the pattern A of a predetermined number of stitches 1-10 and the pattern B of repeated stitches 11-10-11-10 are at first continuously produced in the forward feeding direction. The number of stitches in the pattern B may be optionally determined from the point P in dependence upon the size of buttonhole that the operator desires.
When the pattern B is continuously stitched in a length desired by the operator to reach the point Q, the operator stops the sewing machine and is required to operate another pattern selecting switch designating the combination of patterns C and Ba and then drives again the sewing machine, the pattern C is produced with the predetermined number of stitches 1-30 from the point Q to the point R and then the pattern Ba is continuously produced in the reverse feeding direction with the stitches 31-32-31-32 which are counterparts of the stitches 10-11-10-11 of the pattern B. The operator is, however, required to stop the sewing machine when the last stitch of the pattern Ba has come into alignment at the point S with the initial stitch 9-10 at the point P of the pattern B, so that the patterns may be a complete symmetry on both sides of the vertical center line of the buttonhole, as shown in FIG. 1. And then, the operator is required to operate another pattern selecting switch designating the last pattern Aa with the predetermined number of stitches 1-10, which are counterparts of the stitches 1-10 of the pattern A, and then to drive the sewing machine until the sewing machine is automatically stopped. Thus the buttonhole of pigeon-type is completely stitched.
However, it is to be noted that there is difficulty in placing the last stitch of the pattern Ba into alignment at the point S with the initial stitch 9-10 of the pattern B at the point P as shown in FIGS. 1 and 2, and the machine operator have often failed to do this task, resulting in the deformation of the buttonhole stitches such as shown in FIGS. 3A, 3B and 3C. FIG. 3A shows an example wherein the operator has switched the pattern Ba over to the pattern Aa before the pattern Ba comes to the point P of the pattern B. FIGS. 3B and 3C show examples wherein the operator has switched the pattern Ba over to the pattern Aa after the pattern Ba went past the point P of the pattern B.